In order to drive along a roadway between plowing sites, the operator of a vehicle typically partially raises the snow plow, or other front-end implement, high enough to clear the roadway surface but not so high that the partially raised plowing implement obstructs the driver's view or severely obstructs the flow of cooling air past the plowing implement into the radiator of the vehicle.
Many plows are raised by a chain whose first lower end is attached to a hook supported by an intermediate pivotable section of the plow and whose second upper end is attached to another hook supported by an outer end of a pivot member. A hydraulic cylinder or electric motor, controlled by a control mechanism and activated by the operator, is attached to the pivot member for raising and lowering the pivot member and thereby the plow as desired.
When driving down a bumpy road or over a "pot" hole or other road surface undulation, a chain supported plow typically bounces up into the air from its partially raised position, thereby creating some slack in the chain, and then the plow comes jerking down pulling the chain taut. The amount of slack generated in the chain is dependent upon a number of factors such as the vehicle speed, the vehicle suspension system, the magnitude of the bump or undulation, etc.
If sufficient slack is generated in the chain upon driving over an undulation in the road surface, such chain slack may occasionally cause an unhitching of either the upper or lower end of the chain from one of the hooks. If the bouncing up and down of the plow was not sufficient to cause an unhitching of the chain from the hooks, such bouncing eventually leads to premature chain fatigue and/or chain failure which may occur while driving down the roadway. In either event, if the vehicle is in motion when the chain brakes or unhitches, the plow crashes down onto the roadway. Not only does this cause damage to the lower longitudinal edge of the plow, as the plow slams into the road surface and is subsequently pushed therealong, but the plow may possibly get jammed into the roadway stopping the vehicle suddenly or quickly slowing down the vehicle. The unexpected release of the snow plow perhaps causing an accident thereby injuring the driver or any passenger(s) in the vehicle and/or damaging the plow, the plow mounting structure, or the vehicle.